The photoelectric smoke sensor is equipment for detecting smoke caused by an outbreak of a fire in a space. Specifically, the photoelectric smoke sensor detects smoke flowing into a housing of the photoelectric smoke sensor by light. Such a photoelectric smoke sensor is installed in an indoor space or a space in various types of devices, and detects smoke in the space.
Photoelectric smoke sensors installed in such a space include a sensor described in Patent Document 1. This photoelectric smoke sensor will be roughly described on the basis of FIG. 1. In the description below, upper, lower, right and left sides are based on the state in FIG. 1.
A smoke sensor 1 is composed of a cylinder portion 2 and a flat box portion 3 extended upward from the cylinder portion 2.
The cylinder portion 2 has functions of allowing intrusion of smoke and guiding the smoke into the inside while preventing entry of ambient light into the inside of the smoke sensor 1. A mountain-shaped labyrinth 4 having a mountain shape (a conical shape with the head part cut off) is provided in a lower-surface opening of the cylinder portion 2. The mountain-shaped labyrinth 4 has its center part raised in a shape of a mountain and has a plurality of openings 5 functioning as an introduction port for the smoke and also preventing entry of the ambient light provided in the peripheral edge portion thereof.
The flat box portion 3 has a substantially rectangular solid shape and has a smoke detection function. A lateral width of the flat box portion 3 is the same as an outer diameter of the cylinder portion 2, and the flat box portion 3 extends upward from the cylinder portion 2 so that the center axis of its own matches the center axis of the cylinder portion 2.
In an upper part of the flat box portion 3, a side-face small hole 7 is provided. This side-face small hole 7 functions as an opening when the smoke is led out from the inside of the smoke sensor 1 to the outside. That is, the smoke introduced into the smoke sensor 1 through the opening 5 of the mountain-shaped labyrinth 4 and the side-face small hole (not shown) of the cylinder portion 2 is led out through the side-face small hole 7 of the flat box portion 3. The smoke might flow into the smoke sensor 1 also through the side-face small hole 7.
Inside of the smoke sensor 1, a light emitting element 8 and a light receiving element 9 are provided.
The light emitting element 8 is an element provided by being faced with a detection region AR in the housing of the flat box portion 3 and emitting inspection light to the detection region AR. The light emitting element 8 is provided at a position in an upper part of an internal space of the flat box portion 3 (upper left in FIG. 1) by a light emitting element accommodation portion 11. The light emitting element accommodation portion 11 accommodates the light emitting element 8 so that the inspection light emitted from the light emitting element 8 is emitted only forward. An optical window portion 12 is provided in front of the light emitting element accommodation portion 11.
The light receiving element 9 is provided at a position in the lower left in the internal space of the flat box portion 3 by a light receiving element accommodation portion 13. The light receiving element accommodation portion 13 accommodates the light receiving element 9 in a bottom portion thereof and has an objective lens 14 attached in an upper part thereof.
The light receiving element 9 is provided by being faced with the detection region AR at a position shifted from an optical path of the inspection light of the light emitting element 8 and receives diffused light which is the inspection light diffused by having hit the smoke and detects the smoke. Specifically, the optical axis of the light emitting element 8 and the optical axis of the light receiving element 9 are configured to cross each other at an angle of approximately 120 degrees, and the vicinity of the intersection becomes the smoke detection region AR. As a result, if there is smoke in the detection region AR, the inspection light from the light emitting element 8 is diffused by the smoke, the diffused light reaches the light receiving element 9, and the presence of the smoke is detected.
Between the light emitting element 8 and the light receiving element 9 (at a position left to the detection region AR), a shielding plate 15 is provided for preventing direct entry of the inspection light from the light emitting element 8 into the light receiving element 9 without being diffused.
In the right of the light receiving element accommodation portion 13, two labyrinth pieces 17 and 18 are provided. The labyrinth piece 17 is formed with inclination in an upper right direction and guides an air flow from the lower side to the upper right direction by its lower surface. Moreover, an end portion in the upper direction of the labyrinth piece 17 is bent to an upper left direction. This end portion has a function of leading the air flow raised along an upper face toward the detection region AR. The labyrinth piece 18 is formed with inclination in an upper left direction at a position upper left of the labyrinth piece 17. The labyrinth piece 18 guides the air flow directly from below and the air flow flowing along the inclination of a lower inclined surface 13a of the light receiving element accommodation portion 13 to the upper left direction. In the upper left direction of the labyrinth piece 18, an upper inclined surface 13b of the light receiving element accommodation portion 13 is provided. The air flow flowing toward the upper inclined surface 13b of the light receiving element accommodation portion 13 is directed to the direction of the detection region AR by the inclined surface 13b. 
At a lower end position of the side-face small hole 7 of the flat box portion 3, a labyrinth piece 20 extending substantially to the left is provided. This labyrinth piece 20 is bent at the intermediate position thereof so as to be directed to the upper left direction. The air flow having passed the detection region AR and further rising is narrowed by an upper inclined surface 11a of the light emitting element accommodation portion 11 and the lower inclined surface of the labyrinth piece 20 and reaches the upper surface of the internal space. Then, it is directed toward the side-face small hole 7 by a pressure of the air flow after that and is led out of the side-face small hole 7. Reference numeral 21 denotes an insect screen. Moreover, a labyrinth piece 22 is provided below the labyrinth piece 17.
The above-described mountain-shaped labyrinth 4, the lower inclined surface 13a of the light receiving element accommodation portion 13, the labyrinth pieces 17, 18, 20, and 22 and the like suppress entry of the ambient light into the inside.
By means of the above configuration, the inspection light from the light emitting element 8 is emitted to the detection region AR. At this time, direct incidence of the inspection light into the light receiving element 9 is prevented by the shielding plate 15. The ambient light tries to intrude through the opening 5 of the mountain-shaped labyrinth or the side-face small hole 7, but this ambient light is prevented by the labyrinth pieces 17, 18, 20, and 22 and the like.
If smoke intrudes through the opening 5 of the mountain-shaped labyrinth or the side-face small hole 7 in this state, the smoke intrudes into the detection region AR through the labyrinth pieces 17, 18, 20, and 22 and the like. Then, the presence of the smoke is detected when the inspection light from the light emitting element 8 is diffused by the smoke, and the diffused light reaches the light receiving element 9.    Patent Document: International Publication No. WO2006-112085